A blade damper is essentially a valve or plate that is positioned over an orifice and is used to regulate the flow of air, gas or liquids ("fluids") through the orifice. The blade damper is generally mounted on an axle for rotation within the orifice, with the axle mounted relative to the orifice. One such use of a blade damper occurs within a heat exchanger having a combustor containing a fluidized bed wherein one or more dampers are placed within the heat exchanger to control the flow of air to the fluidized bed.
In general the flow of fluid through an orifice is determined by the pressure differential across the orifice and by the surface area of the orifice. Ideally, when a damper is closed it should not allow any fluid to flow through the orifice; when it is fully open it should not restrict the flow of fluid through the orifice; and, when it is partially open, it should allow fluid to flow through the orifice relative to the percentage opening of the damper. With proper control of pressure, the flow of fluid through the orifice is approximately proportional to the opening of the damper. However, this linear relationship between the flow of fluid through the orifice and the damper opening is often impossible to obtain due leakage of fluid through the damper boundary planes perpendicular to the axle.
Several techniques are known in the prior art for preventing leakage of fluid through an orifice sealed by a blade damper when the damper is closed. For example, the blades of the damper are overlapped with the edge of the orifice, or sealing strips are provided at the edge of the blade. Other techniques are employed to allow for maximum fluid flow through an orifice when the damper blade is fully open. However, none of these techniques have addressed the problem of controlling fluid leakage through boundary planes perpendicular to the axle when the blade damper is partially open.